Effect of Sn grain orientation on electromigration degradation mechanism in high Sn-based Pb-free solders

Electromigration induced damage strongly depends on Sn-grain orientation in Pb-free solders. Rapid depletion of intermetallic compounds and under bump metallurgy led to significant damages caused by the fast diffusion of Cu and Ni along the c axis of Sn crystals. When the c axis of Sn grain is not aligned with the current direction, electromigration (EM) damage is dominated by Sn self-diffusion, which takes longer to occur. This is a direct proof of the highly anisotropic diffusion behavior in Sn. Due to the presence of twin structures and stable Ag3Sn network, SnAg(Cu) solders are less susceptible to grain orientation effects and showed better EM performance than SnCu solders. (C) 2008 American Institute of Physics.